The present invention relates to an electromagnetically coupled microstrip patch (EMCP) antenna element whose feeding patch is capacitively coupled to a feedline. The feeding patch is electromagnetically coupled to a radiating patch. A plurality of such antennas may be combined to make an antenna array.
Microstrip antennas have been used for years as compact radiators. However, they have suffered from a number of deficiencies. For example, they are generally inefficient radiators of electromagnetic radiation; they operate over a narrow bandwidth; and they have required complicated connection techniques to achieve linear and circular polarization, so that fabrication has been difficult.
Some of the above-mentioned problems have been solved. U.S. Pat. No. 3,803,623 discloses a means for making microstrip antennas more efficient radiators of electromagnetic radiation. U.S. Pat. No. 3,987,455 discloses a multiple-element microstrip antenna array having a broad operational bandwidth. U.S. Pat. No. 4,067,016 discloses a circularly polarized microstrip antenna.
The antennas described in the above-mentioned patents still suffer from several deficiencies. They all teach feeding patches directly connected to a feedline.
U.S. Pat. Nos. 4,125,837, 4,125,838, 4,125,839, and 4,316,194 show microstrip antennas in which two feedpoints are employed to achieve circular polarization. Each element of the array has a discontinuity, so that the element has an irregular shape. Consequently, circular polarization at a low axial ratio is achieved. Each element is individually directly coupled via a coaxial feedline.
While the patents mentioned so far have solved a number of problems inherent in microstrip antenna technology, other difficulties have been encountered. For example, while circular polarization has been achieved, two feedpoints are required, and the antenna elements must be directly connected to a feedline. U.S. Pat. No. 4,477,813 discloses a microstrip antenna system with a nonconductively coupled feedline. However, circular polarization is not achieved.
Copending application Ser. No. 623,877, filed June 25, 1984 and commonly assigned with the present application, discloses a broadband circular polarization technique for a microstrip array antenna. While the invention disclosed in this copending application achieves broadband circular polarization, the use of capacitive coupling between the feedline and feeding patch and the use of electromagnetic coupling between the feeding patch and radiating patch is not disclosed.
With the advent of certain technologies, e.g. microwave integrated circuits (MIC,) monolithic microwave integrated circuits (MMIC,) and direct broadcast satellites (DBS,) a need for inexpensive, easily-fabricated antennas operating over a wide bandwidth has arisen. This need also exists for antenna designs capable of operating in different frequency bands. While all of the patents discussed have solved some of the technical problems individually, none has yet provided a microstrip antenna having all of the features necessary for practical applications in certain technologies.